Apparatus for testing light discrimination



Dec. 15, 1959 M. A. BOUMAN APPARATUS FOR TESTING LIGHT DISCRIMINATION 2 Sheets-Sheet 1 Filed March 31, 1955 INVENTOR.

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APPARATUS FOR TESTING LIGHT DISCRIMINATION Filed March :51, 1955 2 Sheets-Sheet 2 INVENTOR.

01/ /V Milling/ V {ll/IVE B M? United States Patent APPARATUS FOR TESTING LIGHT DISCRIMINATION Maarten A. Bouman, Utrecht, Netherlands, assignor to The Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk ()nderzoek Ten 'Behoeve van de Rijksverdediging (The National Defence Research Council T.N.0.), The Hague, Netherlands, a corporation of the Netherlands Application March 31, 1955, Serial No. 498,394

Claims priority, application Netherlands April 3, 1954 3 Claims. (Cl. 88-20) My invention relates to an apparatus for examining the discriminating capacity of human beings between light of different intensity and of ditferent colour.

The main object of my invention is a novel and simple apparatus by means of which several stimuli can be compared simultaneously.

The apparatus consists essentially of two compartments separated by a thin partition wall. The walls of the compartments are covered with a diffusely reflecting white paint as used in photometer spheres-for example zincoxideand provided with openings through which light of adjustable intensity and adjustable colour can be admitted. In the partition wall holes are provided which are so small and close to each other that from some distance they cannot be seen separately.

These openings are arranged in recognizable, for instance geometrical configurations, which may be rectangles or other simple geometrical configurations.

A part of the wall of one of the compartments is left open, so that a window or opening is formed through which the partition wall can be seen.

The partition wall contains a number of geometrical configurations constituted by perforations which hereafter will be referred to as test areas. The arrangement of the holes is preferably identical for the individual configurations but the size of the holes in the individual configurations is different. A person placed at some distance before the apparatus sees the light reflected by the partition wall and the light passing through the openings, which comes from the compartment behind the partition wall. If the illumination in the back compartment is the same as in the front compartment the configurations cannot be seen by the observer. If the luminous intensities of the walls of both compartments are slightly different some of the configurations can be seen and the number of configurations which can be seen is a measure of the capacity of the observer to discriminate between light of different intensity.

The same applies when the back and front compartments are illuminated by light of the same intensity but of different spectro-composition; i.e. of different color.

My invention is further illustrated by a drawing Wherein two embodiments of my new apparatus are shown.

Fig. l is a general View of a first embodiment of the apparatus.

Fig. 2 is a top view, partly in section of the apparatus.

Fig. 3 is a general view of a second embodiment.

Fig. 4 is a detail of the embodiment illustrated in Fig. 3.

In Fig. l, l is a box, 2 is'a slidable partition which can be adjusted. In this partition a number of rectangles 3, 4, 5, 6, 7 are shown, provided with holes which in every individual rectangle are of the same size but of different sizes in the several rectangles. In the side walls a number of openings are made which can be obscured partially or wholly by adjustable lids 11.

These openings are provided at both sides of the partition 2. An incandescent lamp 9 is situated in front of the openings 8 so that the light emerging from this lamp is distributed over both compartments.

In the opposite wall similar openings are made. The walls of both compartments are covered with white dif fusely reflecting paint. In order to compensate for the loss of brightness in the front compartment due to the window 12 a corresponding portion of the walls of the back compartment may be blackened.

In the openings through which the light emerging from the incandescent lamp is admitted into the compartments a milk glass plate is provided in order to promote the uniform distribution of the light.

An observer placed before the apparatus will see the partition wall 2 through the opening 12. This opening is preferably large enough to see a number of the configurations simultaneously. When the illumination in both compartments is very different the observer can clearly see all test areas from which light rays emerge through the window 12 in the direction of his eyes.

When, however, the difference in the intensity of the illumination is made smaller, egg. by adjusting the slides 11, the number of test areas which can be distinguished from the surrounding part of the partition wall becomes less and less. The number of test areas which can be seen at a predetermined slight difference of brightness in the compartments gives a reliable indication of the discriminating capacity of the observer with respect to intensity differences.

Exactly the same procedure applies if the capacity for discriminating between colours is to be examined. The colour of the light in the back compartment can be made different from that in the front compartment by means of filters. The intensity can be adjusted to the same value in both compartments by adjusting the slides It may be remarked that the opening 12 must be lo cated at some distance from the wall 2 and that the general illumination in the room where the examination takes place should not be too high.

If a portion of the walls of the back compartment is blackened for the reasons stated above this blackened part should not be visible through the holes in the partition wall.

Preferably the small openings in the partition wall are made so that the width thereof at the backside of the partition wall is larger than at the frontside. Under these circumstances the walls of these holes are not visible.

The configurations constituted by the arrangement of the holes in the partition wall need not be squares or, other simple geometric configurations but can be letters or ciphers, subjected however to the condition that they,

the line C C corresponding with the colour of the test area depends in a well known manner on the colour and the intensities of the illumination of the wall in the back compartment and the frontside of the partition.

If the intensity of colour 0, is B that of colour C is B and the fraction of the test area covered by the holes is a, then the resulting brightness B of T is B=(l-oa)B +ozB If B =B =B, then the colour C of the test area is found by the equation CC :CC =a:(1-a) Hence when observed from a sufficient distancelthe' 3 sensation corresponding to C B can be compared with that of 0,3.

The diameter of the holes in the partition wall may vary fromabout 0.1 to about 1 mm. and the centers of the holes may be 1.5 mm. apart from each other.

The actual dimensions ofan apparatus that has been used with very satisfactory results were as follows:

The area of the partition wall comprising the test areas was x centimetres, the test areas themselves measuring 1 x 5 cm. The test areas are separated by non-perforated strips of the partition wall. The opening 12 is of such sizethat when observed from a distance of about 5 metres the light from six test areas reaches theeyes of the observer.

For technical reasons a can hardly be made larger than /z. The value a=l can be added by cutting out the whole test area. Whenthe test areamust cover a larger'part of the line C 'C than for the region of a fraction of the test area may be blackened. If for instance the fraction of the test area corresponding to the holes is on a fraction s may be blackened. Then if B is the brightness of the surroundings of the test area and B the brightness of the walls of the back compart ment, the brightness B of the test area will be The condition for equal brightness of'the'test'area and its-surroundings is B =B, oraB (oa+fi)B and thus So by providing test areas having different ozS and fis any colour between C and C can be compared with 0,.

I Obviously the blackened partsof the frontside of the test area must consist of uniformly distributed small black areas.

Ifdesiredthe surroundingsof the test area could be blackened partially by uniformly. distributed small black areas. When y is the blackened fraction of this part of the plate B in the formulae is, to be replaced by B 'The apparatus'illustratedin Fig. 3 is of the same general type as that of Fig. 1. The shape of the compartmentsin this case, however, 'is nearly spherical in order to'improve the uniformity of the illumination (brightne's's)'.. As in Fig. 1 there are a' front compartment indicated by 30 and aback compartment 31.

Between the spheres a fiat partition wall 32 is arrangedwh'ich isprovided with a number of test areas 33 of the same type as alreadyhave been described in connection with Fig. 1.

The partition wall 32 is slidably mounted in suitable guides 34,35. The part 36 of the back compartment opposite the partition wall is flattened. The opening 37 in the front compartment, the part of the partition wall between the spheres 3t) and 31' and the flattened part 36 have the same sizev and shape. Thus the shapes of both spherical compartments are identical. .To compensate forthe loss of brightness in the front compartment 30-,

due toatbe view opening 37, the'backside of the partition Wall. is ckene In each offthercompartments the lightqof fourincandescent lamps is introduced by. means of optical systems having their focus at 38 and 39 respectively. Preferably this focus should be located as nearly oppositeas possible to the test areas and the-flattened part 36 respectively in order to obtain the greatest possible brightness combined with auniform illumination of said parts o e mpa men s- 1 The incandescent lamps of which only two are shown in each of the compartments are indicated at 40, 41 and 42, 43.

They are mounted in little boxes 44, 45, each provided with a partition 46, 47 respectively, having four openings 48, 49 respectively.

Opposite each of the lamps an optical system is located consisting of a condenser lens 50, a filter 51 and a polaroid 52. Instead of a polaroid an adjustablediaphragm or' a neutral wedge maybe used. As an alternative the currents in the lamps may be adjustable. All optical systems are of the same type and a description of the remaining systems is therefore superfluous.

The optical systems are mounted in tubular members 53 which are welded on the outer surface of the compartments.

The boxes 44 and 45 wherein the lamps are-mounted are provided with holes at 54, 55 and 56, 57 respectively.

Bars 58 and 59 extend through the holes 54, 5S and 56, 57 and carry the boxes 44 and 45.

In the box 45 a rotatable member 60 is mounted. This member has the shape shown in Fig. 4.

In this figure the small circles indicated by the reference numbers 61, 62, 63 and 64 indicate the positions ofthe four incandescent lamps in the box 45.

In front of the apparatus a third compartment is provided. This compartment is illuminated by a number of incandescent lamps 66, 65 and the inner surfaces are painted white, whereas the surfaces 68 and 69 areblackcried for obvious reasons.

The brightness of the inner surfaces of the third compartment is adjusted so as to be equal to the brightness ofthe spheres 30 and 31. V

Inorder totest the equality of the brightness of the spheres 30 and 31, a test area of the partition is used for which 11:1. If the surroundings of this testareacannotbe seen against the background constituted by the flattened portion 36 the brightness in both spheres is the same. 7 7

To obtain colours of the same brightness the member 60 is used. The procedure is as follows: 7

Circle 61 represents the lamp producing White light and the other circles represent the lamps producing coloured light. The white lamp and one of the coloured lamps are turned on and then the member 60 is rotated. The intensities of the lamps are adjusted until the flickering is reduced to a minimum. Then the brightnesses of the white illumination and the coloured illumination are the same. Obviously the equality of the brightness thus obtained has a subjective character and as a rule will be different for different human beings.

I claim:

1. An apparatus for testing light discrimination comprising two adjacent compartments, a partition dividing said compartments, said partition having groups'of a plurality of small perforations arranged in recognizableconfigurations, the perforations comprising each group being of equal diameter and the perforations being of different diameters for each group, a viewing opening in one of said compartments opposite said partition, said partition beingdirectly viewable from said viewing opening, means for. illuminating each of said compartments, and means for adjustin said illumination whereby diiferent light;

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS 'Bijur Feb. 13, 1900 Ives May 20, 1924 Sheard Dec. 8, 1925 Bauersfeld et a1. Mar. 10, 1931 Morris Nov. 9, 1948 Justice Mar. 21, 1950 Alexander Apr. 6, 1954 6 FOREIGN PATENTS Great Britain of 1898 Germany Apr. 24, 1940 OTHER REFERENCES New York, 1922, pages 114-416.

in Division 7.)

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